The present invention relates to a sensor device, a use and a method of operating such a sensor device.
Sensor devices of the general kind set forth are known from the state of the art, for example from alarm technology, and have a pyrodetector which operates on an infrared basis and which is usually configured as a motion sensor and which outputs a detector signal as a reaction to a significant change in an infrared radiation pattern which is incident on the sensor. Connected downstream of such a sensor device of the general kind set forth there are then suitable consumers, signal units or other functional units to be controlled, for example lighting arrangements, monitoring cameras, alarm installations or the like units.
In addition, so-called sensor lights are known from the state of the art, more specifically motion sensor-controlled light units whichxe2x80x94with a correspondingly low level of external ambient brightnessxe2x80x94can usually be activated in response to the movement of a person. Sensor lights of that kind also have a passive infrared sensor (PIR) with pyroelectric detector elements; usually however lighting arrangements of that kind are not operated regularly in daylight conditions. As however the pyroelectric detectors generally react exclusively to infrared radiation they are also suitable for motion detection in daylight.
In practical tests however in particular a very bright external ambient condition, that is to say a high level of radiation in the visible ambient light range, has been found to be detrimental in terms of reliable operation of pyroelectric detectors, more specifically in such a way thatxe2x80x94in the absence of any motion signalxe2x80x94they trigger off fault switching procedures which, as tests on which the present invention is based have shown, are usually caused by fluctuations in brightness. Common pyroelectric sensors (or pyrosensors or thermopile sensors) generate an evaluatable signal when the amount of radiation which is incident on detection surfaces of the sensor changes; that signal change is evaluated specifically for the purposes of motion detection. To avoid disturbances by such signals which are not caused by the movement of a person or an object, current pyrosensors have a filter which passes only radiation in the relevant infrared spectral ranges (for example between 8 and 14 micrometers); radiation from other spectral rangesxe2x80x94with visible light between about 380 and 760 nanometersxe2x80x94is filtered out by reflection or absorption.
However tests in the context of the present invention have shown that, with very large amounts of radiation being involved, irrespective of the spectral range, the entrance window of the detector, which is in the form of a mass filter, increases slightly in temperature, more specifically due to those radiation components which are not transmitted or reflected. That absorbed heat is then passed to the respective inner or outer surface of the sensor and is there irradiated again from the filter in the form of heat radiation. That can then activate the detector surfaces of the sensor, which is not wanted. While, in the event of very slow changes in the overall irradiation strength, the heat dissipation in the filter and a band pass-form amplification characteristic of the sensors prevent fault switching procedures, a (fault) signal is however produced in particular when the radiation strength changes in a frequency within the band pass, usually between 0.1 and 10 Hz, and so much heat is produced in the filter by correspondingly great changes that an evaluatable signal is produced. As a result the sensor then detects a signal without a movement in the detection region having occurred.
In accordance with the invention it has been found that those troubles occur with brightness fluctuations from about 2000 lux, while in particular with a high level of brightnessxe2x80x94solar radiation in the summer timexe2x80x94shadows due to scarcely visible hazy clouds can produce changes of that kind by some 1000 lux, without such changes being perceived for example by a human being.
As however conventional sensor lights are usually operated in the brightness ranges which are below 2000 lux (therefore also use thereof as so-called xe2x80x98twilight switchesxe2x80x99), it was not possible in any case here for any fault switching procedures to occur due to significant fluctuations in brightness .
For effective operation in daylight, which is substantially trouble-free (safeguarded against fault switching procedures) however existing sensor devices are disadvantageous and need improvement and in particular the unintentional sensor activations which are caused by fluctuations in brightness are to be avoided.
Therefore the object of the present invention is to improve a sensor device of the general kind set forth in regard to its detection and switching characteristics in the event of large absolute changes in ambient brightness and in particular to avoid fault switching procedures which are caused by the brightness involved.
That object is attained by a movement sensor device comprising pyroelectric sensor adjusted to operate in daylight, and an electronic evaluation device connected downstream of the sensor and designed to generate a control signal (S) as a reaction to a detector signal of the sensor relative to a threshold value, wherein the electronic evaluation device comprises means for measuring a daylight-ambient luminosity, and compensating means designed in such a way that they carry out a compensating threshold value change in the threshold value and/or a compensating change in the detector signal as a reaction to a predetermined change in the daylight-ambient luminosity, the electronic evaluation device being designed in such a way that the compensating means only act if a change in the daylight-ambient luminosity is more than 1,000 lux in a band-pass filter-like response range of the sensor.
Advantageously, for the first time means are used for directly measuring the ambient brightness or a change therein and that detected brightness variation is used in order with the compensating means according to the invention to provide dynamic influencing, corresponding to current light conditions, of the switching characteristic of the sensor. In that respect direct measurement of the change in brightness (or the fluctuation in radiation) makes it possible to establish the relationship between the fluctuation in radiation,and the sensor signal (or the change therein as a reaction to the fluctuation in radiation) and to compensate for same by calculation or numerically (that is to say changes in the ambient conditions).
In the specific configuration of the measurement means there is on the one hand the possibility of using a CCD-chip or CMOS-chipxe2x80x94which is in any case possibly present in the context of a use provided with an image pick-up unitxe2x80x94for ascertaining the absolute change in the brightness signal (in the visible spectral range); in that way the brightness signal is available for taking account in accordance with the invention, in a simple manner and without involving additional hardware expenditure.
A possible alternative is that of using an additional pyrodetector which further preferably is modelled on or is a reproduction of the pyroelectric sensor in terms of its detection properties, wherein with that additional pyrodetector the actual useful signal is faded out. That means that the additional pyrodetector measures only the disturbances to the useful signal, caused by other effects to be compensated, as can occur for example due to light, heat or electromagnetic waves (changes in the ambient conditions). In other words, the same type of sensor which is used in accordance with this development as that used for detecting the useful signal is blocked with suitable filter means for the useful signal and therefore serves only to detect the system-governed disturbances which arise out of ambient factors.
As a result it can then be provided that fault switching procedures which for example are due to considerable fluctuations in brightness can be suppressed.
In that respect it is in accordance with the invention, by suitably influencing a switching threshold which influences the switching procedure, to produce the compensation effect and/or to correct a sensor output signal by corresponding brightness-dependent correction values; they may possibly also be present in table form and they can be read out as required.
Independent protection in accordance with the present invention is claimed for a configuration which implements the compensation effect in a manner in accordance with the invention by optical filter means. Those filter means on the one hand reduce the amount of radiation incident on a detector element so that the risk of brightness-caused error switching procedures is eliminated, while on the other hand the filter means according to the invention ensure that the detection range of the useful radiation in the infrared range is independent of a specific angle of incidence on a detector element of the sensor and remains constant over a minimum angular region
Thus it is particularly preferred for threshold values or threshold value ranges for producing the control signal to be dynamically increased or reduced with the compensating means; it is further preferred to adjust a current threshold value to an ambient light level.
While light detectors or photodetectors of any kind which permit radiation detection of the specified high levels of brightness and large fluctuations in brightness are suitable for implementation of the invention, it is particularly preferable, for the purposes of brightness measurement, to use the exposure device of a CCD-camera element or the like integrated image pick-up element, which in the context of an overall installation is in any case possibly already connected downstream of the sensor device as a functional unit. A functional unit of that kind with a sensor device of the general kind set forth is to be found in the applicants"" German utility model DE 297 05 569 and is to be deemed to be incorporated into the disclosure of the present application in respect of the functional implementation of the functional unit, including the image pick-up unit.
In accordance with the invention, that not only uses the property of the CCD-element of being able to pick up and resolve large fluctuations in brightness, but also such an arrangement renders a separate sensor for detecting interference factors redundant.
In accordance with the independent configuration using optical filter means, they are preferably implemented by means of a removable filter cap which in a further preferred feature is dome-shaped, dome-shaped and/or provided with a portion of hemispherical shape. In an advantageous manner in accordance with the invention, polyethylene has proved itself as the material for such a filter cap, wherein in a further preferred feature that material is provided with a carbon black addition  less than 1%, further preferably  less than 0.5%.
It is also in accordance with the present invention, in a particular development, for the wall thickness of the filter (or the filter cap) to be variable in dependence on angle and preferably to be so designed that a uniform range is achieved in the entire detection region; here in particular in accordance with the design configuration involved the filter thickness is so set that the absorption is greater in the central region and less in the edge region, in each case in relation to the angular region according to the invention.
In a particularly advantageous fashion this optical filter configuration also ensures that existing systems can be retrofitted without any difficulty, more specifically by virtue of the filter means according to the invention being designed to fit on to conventional, commercially available pyrodetectors.